Following Colonel O'Neill, CaptainCarter and Teal'c's strange behavior since their return from Oannes, Doctor MacKenzie uses a recorder with specific sounds to increase their level of concentration. O'Neill is upset, but Teal'c reacts when he sees flashes with Daniel Jackson burning in fire among orange bubbles. MacKenzie notices the conflict as all of them state that Daniel is alive and yet Daniel is dead. He tells that both realities can't be true, yet both seem to be.

To solve the issue, MacKenze suggests to use hypnosis to see why three hours and half are missing in their memories and why all of them are conditionned to give specific answers. Carter volunteers. Soon after, using hypnosis, MacKenzie makes Carter retrieving memory of what happened after Daniel's "death".

Noticing an increase of schizophrenia, MacKenzie sends Daniel in a mental facility. After Goa'uld killing organisms passed from Daniel to Teal'c, Daniel argues with Dr. MacKenzie to let him go as he's not suffuring anymore. Later, MacKenzie reports to the SGC that Daniel's behavior has changed. After O'Neill's visit to Daniel, MacKenzie frees Daniel from the mental facility.

After ApophisbrainwashedTeal'c (SG1: "Enemies"), he's meditating when O'Neill, Dr. MacKenzie and General Hammond come into the secure room. Teal'c seems to have recover and pledges allegiance once more to the Tau'ri. He says that Dr. MacKenzie has convinced him that Apophis is a false god. MacKenzie says that Teal'c convinced himself. General Hammond asks MacKenzie about what he thinks regarding Teal'c resuming duty, and MacKenzie shrugs, letting O'Neill making the decision.

Soon after, Bra'tac meets Teal'c and realizes that Teal'c has deceived all of them.

"MacKenzie" is spelled differently in different episodes. In "Fire and Water" and "Threshold", it is spelled "McKenzie" in English subtitles as well as ending credits. In other episodes, it's spelled "MacKenzie".